The mechanical, electrical, optical, chemical and thermal properties of diamond make the creation of diamond thin films desirable for many applications. Such films are sought for applications ranging from wear-resistant coatings to substrates for semiconductor devices See Editorial, "Molecule of the Year," Science 250, 1637, 1640-41 (Dec. 21, 1990). Currently, however, diamond thin films are only created using vapor deposition techniques and only as polycrystalline films. See W. Yarbrough and R. Messier, Current Issues and Problems in the Chemical Vapor Deposition of Diamond, Science 247, 688-96 (Feb. 9, 1990).
Diamond thin films have been successfully grown by a variety of low pressure and low temperature chemical vapor deposition (CVD) methods, such as filament assisted CVD, plasma CVD, and combustion flames. See Devaries, Ann. Rev. Mater. Sci. 17, 161 (1987); Matsumoto et al, J. Mat. Sci. 18, 1823 (1988). In these methods, typically a mixture of hydrocarbons such as CH.sub.4 and C.sub.2 H.sub.2 and hydrogen (98-99.5% by volume) is passed over heated (700.degree.-1000.degree. C.) substrates such as silicon, nickel, copper, tungsten, and silicon carbide. During the process, both diamond and graphite are deposited. However, preferential etching of graphite by hydrogen leaves diamond crystallites which grow further to form polycrystalline films. Single crystal diamond thin films have been grown epitaxially only on diamond substrates, where all three axes of the film are aligned with respect to the underlying substrate (see Geis et al, IEEE-Electron Device Lett. EDL-8, 341 (1987); M. W. Geis, Materials Res. Soc. Pro., 162, 15 (1990)).
A single crystal diamond substrate was reported as epitaxially grown using CVD on a silicon (Si) substrate having a silicon carbide (SiC) intermediate layer by Imai et al in U.S. Pat. No. 4,863,529. However, a SiC intermediary layer tends to be produced any time a diamond film is grown using CVD on a Si substrate. See Spear, Diamond--Ceramic Coating of the Future, J. Am. Ceram. Soc., 72(2) 171-191 (1989). The CVD method described required high pressures and high temperatures and deposited a diamond thin film onto a SiC intermediate layer. Typically the diamond resulting from CVD methods contains defects such as twins and stacking faults.
In view of the foregoing, an object of the present invention is to provide a novel method for forming diamond thin films which overcomes problems inherent in conventional CVD techniques.